The first obvious use is in pulling. It’s a great way to pull for an initial 500+ damage, you just have to remember to have it equipped before you are ready to pull as it has a cooldown when you first equip it. After use, it also has a 3 minute cooldown before it can be used again.

The second place I have found it useful is for Devastate spam. If I’m in a fight where I can’t spam Heroic Strike, I can swap this in to use on my Devastates. I don’t however think about do so in fights where I need the added survivability or mitigation from [item]King’s Defender[/item] or [item]The Sun Eater[/item].

I haven’t enchanted my Decapitator yet, but I’ll either slap on Potency (+20 str) or Major Striking (+7 damage).

Oh, and here’s a nifty macro for Using the Decapitator when I have it equipped or my regular ranged weapons otherwise:

Another interesting effect of this macro is that using The Decapitator is instant, but it will also perform your ranged attack as well (if you have time to get it off with the now aggro’d mob running towards you)